Dangling bonds are an inherent nature of semiconductor surfaces. Such dangling bonds cause a variety of problems in the fabrication of solid-state devices on semiconductor substrates. They act as reaction sites for chemical reactions and create surface states that cause the observed properties of electronic devices to vary from their design specifications. On a semiconductor surface, dangling bonds adsorb oxygen, water, or carbon dioxide, and a layer of silicon dioxide (the so-called xe2x80x9cnative oxidexe2x80x9d) is formed as soon as the surface is exposed to air.
When a clean silicon(001) surface is kept in ultrahigh vacuum, it has little chance for adsorption or reaction with external species. Under such conditions, the surface undergoes reconstruction to reduce its energy. Each atom on a reconstructed Si(001):2xc3x971 surface has one dangling bond and shares a dimer bond with a neighboring surface atom, as shown in FIG. 1(a). Electronically, surface states originate from dangling bonds and strained surface bonds (i.e. dimer bonds and back bonds) and often pin the surface Fermi level, causing surface band bending. When a metal is deposited on the Si(001) surface, surface states (now more appropriately, interface states) pin the interface Fermi level, making the Schottky barrier height less dependent on metal work function and semiconductor electron affinity and instead, the barrier height is controlled by surface states.
The concept of xe2x80x9cvalence-mendingxe2x80x9d was proposed to eliminate dangling bonds on semiconductor surfaces. For the Si(001) surface, valence-mending atoms include Group VI atoms sulfur (S), selenium (Se) and tellurium (Te). They can bridge between two surface atoms and nicely terminate dangling bonds and relax strained bonds on Si(001), as shown in FIG. 1(b). This structure is often noted as a 1xc3x971 reconstruction. The difficulty with valence mending is controlling the amount of passivating agent that is incorporated so that a new layer of material that significantly interferes with the intrinsic properties of the semiconductor substrate is not built up. Therefore, there exists a need for an effective method of passivating a semiconductor while concomitantly minimizing any carry over effects from the passivation itself.
The present invention provides an improved method for passivating a semiconductor surface.
In one form, the present invention is a method for passivating a semiconductor surface with a monolayer of passivating agent including the steps of placing a semiconductor substrate, having at least one surface, in a chamber and heating the semiconductor substrate to a temperature. The semiconductor substrate is then exposed to a passivating agent for a period of time sufficient to react with substantially all of the surface, and the partial pressure of the passivating agent is such that the passivating agent will not condense at the temperature of the substrate. As a result of this treatment the presence of surface states is greatly reduced.
In another form, the present invention is a method for manufacture of a semiconductor device with a low Schottky barrier including the steps of placing an n-type semiconductor substrate having at least one surface in a chamber and heating the semiconductor substrate to a temperature. The semiconductor substrate is then exposed to a passivating agent for a period of time sufficient to react with substantially all of the surface, and the partial pressure of the passivating agent is such that the passivating agent will not condense at the temperature of the substrate. As a result of this treatment the presence of surface states is greatly reduced. A portion of the semiconductor surface is then metallized with a metal having a work function whose magnitude is greater than the magnitude of the electron affinity of the semiconductor substrate.
In another form, the present invention is a method for manufacture of a semiconductor device with a low Schottky barrier including the steps of placing a p-type semiconductor substrate having at least one surface in a chamber and heating the semiconductor substrate to a temperature. The semiconductor substrate is then exposed to a passivating agent for a period of time sufficient to react with substantially all of the surface, and the partial pressure of the passivating agent is such that the passivating agent will not condense at the temperature of the substrate. As a result of this treatment the presence of surface states is greatly reduced. A portion of the semiconductor surface is then metallized with a metal having a work function whose magnitude is less than the sum of the magnitude of the electron affinity and the band gap of the semiconductor substrate.
Yet another form of the present invention is a method for manufacture of a semiconductor device with improved ohmic contacts comprising the steps of placing an n-type semiconductor substrate having at least one surface in a chamber and heating the semiconductor substrate to a temperature. The semiconductor substrate is then exposed to a passivating agent for a period of time sufficient to react with substantially all of the surface, and the partial pressure of the passivating agent is such that the passivating agent will not condense at the temperature of the substrate. As a result of this treatment the presence of surface states is greatly reduced. A portion of the semiconductor surface is then metallized with a metal having a work function whose magnitude is less than the magnitude of the electron affinity of the n-type semiconductor substrate.
Still another form of the present invention is a method for manufacture of a semiconductor device with improved ohmic contacts including the steps of placing an p-type semiconductor substrate having at least one surface in a chamber and heating the semiconductor substrate to a temperature. The semiconductor substrate is exposed to a passivating agent for a period of time sufficient to react with substantially all of the surface, and the partial pressure of the passivating agent is such that the passivating agent will not condense at the temperature of the substrate. As a result of this treatment the presence of surface states is greatly reduced. A portion of the semiconductor surface is then metallized with a metal having a work function whose magnitude is greater than the sum of the magnitude of the electron affinity and the band gap of the p-type semiconductor substrate.
Those skilled in the art will further appreciate the advantages and superior features of the passivation methods of the present invention upon reading the detailed description that follows in conjunction with the drawings.